2-Butoxyethanol (BE) causes acute hemolytic anemia in rats and metabolic activation of BE to butoxyacetic acid (BAA) is a prerequisite for the development of anemia. To assess the potential health risks of humans exposed to BE, studies were designed to determine the in vitro effect of BAA on RBCs from 10 mammalian species. Blood samples from various mammals were incubated with BAA at a concentration of 0, 1, or 2 mM and kept at 37oC in a gently shaking water bath. Complete blood counts were determined at 0, 1, 2 and 4 hr. BAA caused a time- and concentration- dependent increase in MCV and HCT (followed by hemolysis in certain species), in rats, mice and hamster, rabbits, and baboons. In contrast, blood from pigs, dogs and cats, guinea pigs, and humans, was minimally affected by BAA. These results were confirmed in guinea pigs and rats in vivo. Gavage administration of 250 mg BE/kg to rats resulted in no significant change in these parameters in guinea pigs.